This invention in general relates to fiber optic communication systems and in particular to the structure of components for coupling two or more optical fibers which individually can carry information signals in the form of one or more modulated electomagnetic waves of preassigned wavelength.
Optical fibers have become and will continue developing as an extremely attractive transmission medium for use in the communication industry primarily because of their ability to carry hundreds of times more information than other more conventional media of equivalent size. Paradoxically, the reason which makes optical fibers so attractive also accounts for many of the obstacles to their practical use in large scale communication systems in which their capacities can be fully exploited. For unlike copper wire connectors requiring only a reliable physical contact, optical fibers of hair-like size wherever coupled in a system with other larger components or other fibers require a great deal of precision and the consequence of poor coupling is inherently large signal or information loss.
There are many instances in a system where coupling errors can arise. For example, multiple access requires tapping a single fiber optic link with couplers that are easy to use in the field. Also, combining modulated signals from multiple light sources into a single fiber to increase effective data rates and to permit communication between a number of stations requires couplers in the form of adequate multiplexer/demultiplexers.
To solve some of these coupling problems with tolerable losses, those skilled in the art have developed a class of connectors sometimes referred to as expanded-beam or imaging type connectors of the sort described in, for example, U.S. Pat. Nos. 4,183,618 and 4,186,995 and in an article entitled, "Connectors That Stretch" appearing in the October, 1980 issue of Optical Spectra.
The essence of the expanded-beam type connector is to use two similar connector halves performing like and reversible optical functions. One is used to enlarge and collimate or roughly collimate radiation emerging from a source fiber (or fibers) accurately placed in one half of the connector at the focus of a lens thereof. The other connector half similar in design to the first half, but which may in fact be scaled to be larger, accepts the expanded beam from the first connector half and focuses it into a receiving fiber end located at its axial focus. With this arrangement, the task of optical alignment becomes one of mechanically aligning relatively large beam cross sections rather than small fiber ends as is done in strictly mechanical or butt-type connectors. With such connectors, however, the burden on optical performance and related mechanical geometry is great and must be maintained to a high degree of precision integrated into the connector to assure that the connector itself does not create high losses. As an example, the permissible angular tilt between the lens surfaces of such connectors must be maintained to tolerances on the order of tenths of a degree if losses are not to exceed 0.5 db. Other dimensional requirements demanding adherence to exacting tolerances include the axial locations of the focal point behind any lens surfaces and, as well, laterally with respect to the optical axis; the separation between the connector halves' lens surfaces; and the axial and lateral alignment of the lens surfaces. In addition to the exacting tolerances required on the axial separation between the connector lens surfaces, the separation itself is comparatively small, approximately twice the focal length divided by the refractive index, thus making it difficult to introduce beamsplitters between the connector halves for purposes of multiplexing and demultiplexing. Thus, the expanded beam type connector in its known form is relatively difficult to manufacture and use in fiber optic communication networks for certain purposes. Consequently, it is a primary object of the present invention to provide an improved imaging type optical fiber connector.
It is another object of the present invention to provide an imaging type connector with relatively less demanding manufacturing tolerances.
It is yet another object of the present invention to provide an imaging type fiber optic connector having increased separation between its lens surfaces compared to known connectors.
Another object of the present invention is to provide a fiber optic multiplexer/demultiplexer.
Another object of the present invention is to provide an imaging type connector whose throughput is more tolerant of variations in certain parameters of optical fibers which it connects.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. The invention, accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts exemplified in the detailed disclosure which follows.